Liquid phase exfoliation of bismuth nanosheets for flexible all-solid-state supercapacitors with high energy density

Two-dimensional (2D) layered bismuth (Bi) with a thickness-dependent direct bandgap (0–0.55 eV) has attracted ever-increasing research interest in electronics, energy storage and conversion devices. However, few-layer Bi nanosheets (NSs) are easily oxidized under ambient conditions. Searching for a convenient and low-cost strategy to produce high-quality few-layer NSs in large scale is of great importance to prompt its practical applications. Herein we report that the liquid-phase exfoliation method with acetone solvent is suitable for fabricating 2D thin and low-oxidized Bi NSs. Next, we assemble the produced Bi NSs into all-solid-state supercapacitors (ASSPs). The as-prepared devices exhibit a volumetric capacitance of 36.8 F cm−3, together with excellent volumetric energy and power densities. The volumetric capacity can be further enhanced up to 68.7 F cm−3 by compositing with CNTs. The maximum volumetric energy and power densities are 9.5 mW h cm−3 and 203.2 W cm−3, respectively. Moreover, we demonstrate that the Bi/CNT devices exhibit outstanding flexibility (79.0% retention of the initial capacitance at 180° bending) and superior cycling stability (82.2% retention of the initial capacitance after 20 000 cycles), demonstrating the great potential of Bi/CNTs for high-performance flexible ASSPs.